This application is an improvement of the invention described in United States patent application Ser. No. 07/392,680; filed Aug. 11, 1989, now U.S. Pat. No. 5,012,289; titled Toner Metering Apparatus, and assigned to the same assignee to which this application is assigned. That apparatus has a rotating roller interacting with three flaps to meter toner as required both to and away from a developer roller chamber and a toner supply chamber. Air pressure created by the rotating roller is reduced by a vent between the two chambers. Vents, however, can become clogged. A device which inherently eliminates the pressure differential is more reliable and is potentially less expensive.
The apparatus of the foregoing patent application is the only closely similar structure known, and it has a symmetrical rotating roller and employs venting. This invention employs a roller which is non-symmetrical along its length. U.S. Pat. No. 3,918,839 to Blackwell et al is of interest only in that it shows a non-symmetrical blade, but not used for toner metering.